Modeling Mantle Heterogeneity Development in Earth’s Mantle Using Multidisciplinary Approaches

Abstract:

The process of subduction provides continuous chemical and thermal heterogeneity to Earth’s mantle. How heterogeneity is stirred, stretched and distributed depends on the detail of mantle convection as well as chemical and physical properties of mantle materials. Seismic observations have revealed heterogeneities in Earth’s mantle at varying scales. Seismic velocities are controlled by physical parameters such as density, bulk modulus and shear modulus, which are a function of temperature, pressure and composition. Thus, understanding the origin of seismic heterogeneities play an important role in understanding the thermal and chemical state of the present Earth’s mantle. Originating from the CIDER 2014 workshop, our goal is to take a multidisciplinary approach to tackle a variety of questions, foremost what length scales of heterogeneity might we expect from the convecting process and how do they manifest themselves in seismic imaging. This touches upon fundamental issues such as the composition of the mantle, the nature of stirring and mixing, and the nature of large-scale mantle upwellings (LLSVPs). We will investigate the development of heterogeneity in response to various compositions and redox states using existing and new thermochemical mantle convection simulations, and test the sensitivity of seismic measurements to different length scales of chemical heterogeneity. We try to reconcile large differences in length scales of heterogeneity as well as fractional perturbations of seismic velocity and density predicted by tomography and scattering seismic experiments. Preliminary results from the CIDER workshop initiate with conversion of geodynamic models to profiles of seismic velocity and density which are then taken as input models to predict multiply scattered, high frequency, P wave coda envelopes synthesized by a radiative transport technique. The predicted sensitivity of P coda envelopes to varying chemical compositions and heterogeneity length scales are used to constrain mantle composition and heterogeneity. We see that increased density contrast between components, increases the length scale of heterogeneity. Extensions of this work will attempt to systematically incorporate isotope and trace element data obtained by previous studies to sample mantle heterogeneities.